A coastal cave with turquoise waters found in western Portugal may have once served as a fishing hub and homesite for Neanderthals between 86,000 and 106,000 years ago. The discovery of charred pine, marine mammal remains, and shells from ocean invertebrates add to the evidence Neanderthals hunted, fished, and gathered seafood like early Modern humans.

Modern humans, our closest relatives, adapted to coastal life in southern Africa as long ago as 160,000 years, an adaptation to seafood rich in fatty acids that some research suggests led to enhanced cognitive development in our early relatives. This, in turn, helped to advance technology and cultural innovations during the Middle Stone Age, allowing our ancestors to expand out of Africa and outcompete other early humans.

"The theory is that the consumption of aquatic foods by people living in Africa 100,000 to 200,000 ago would have led to brain development and more advanced intelligence, which in turn would explain why their descendants spreading into Eurasia would have easily 'overtook' Neandertals and 'overtake' their territory, leading them to extinction," study author João Zilhao told IFLscience. 

But did Neanderthals also share this love of the sea and its nutrient-rich food?

To find out, an international team of researchers excavated the Portuguese Figueira Brava site, a three-entranced coastal cave system. Here they found an “exceptionally well-preserved record of Neanderthal coastal resource exploitation” evidenced by the remains of mollusks, crustaceans, fish, birds, tortoises, and both marine and land mammals. The record shows a history of intense, systematic use by Neanderthals during the Last Interglacial period that lasted over the course of thousands of years.

Other Neanderthal sites with shellfish remains have been discovered in Europe, including one in Gibraltar along Spain’s southern Mediterranean coast, and Grotta dei Moscerini on the west coast of Italy. These sites contain scatters of artifacts, shellfish, and some marine mammals dating to between 100,000 years and 40,000 years ago, suggesting Neanderthals did indeed utilize the seas as a resource, long before modern humans showed up in these parts. The amount of food residue found at Figueira Brava exceeds levels found at other sites and provides evidence of marine adaptation mostly only seen in contemporary modern humans living in southern Africa.

The findings, which are reported in Science, add “to the evidence that no categorical distinction in behavior, cognition, culture, subsistence or technology exists between Neandertals and coeval African populations, which, combined with the evidence for extensive interbreeding at the time of contact and the persistence among present-day humans of up to 70 percent of the Neandertals’ genome, implies that we are dealing with populations of the same species," said Zilhao. 

"Put another way, Neandertals are Homo sapiens too." 

The researchers add that their findings close a behavioral gap between modern humans and their closest evolutionary cousins, both of whom relied on the ocean in much the same way during the Middle Stone Age. These fisher-hunter-gatherers were not only widespread but they also likely relied on the sea earlier than previous records indicate. As some Neanderthal groups were able to live in Mediterranean climates removed from mammoth steppes, their access to reliable resources may have triggered growth and made groups more socially complex.

This rise in modern humans has helped to explain the out-of-Africa expansion of modern humans and its role in the disappearance of Neanderthals and other “archaic Eurasian humans”. But knowing that Neanderthals also relied heavily on marine resources may influence what we know about the extinction of such species.

An analysis of when shellfish were gathered is anticipated as a next step by the researchers in determining the vital role marine resources may have played in the evolution and daily lives of Neanderthals.